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Definition of pinnule in US English:

pinnule

noun

Botany

1A secondary division of a pinnate leaf, especially of a fern.

‘If the primary pinnae are divided, then the individual divisions are known as pinnules.’

‘They are commonly referred to as the Lip Ferns because the sori are borne at the margins of the pinnules and the leaf margins themselves are often reflexed to form false indusia that protect the sori.’

‘Lepidopteris is a bipinnate frond whose pinnules resemble some species of Alethopteris.’

‘The most common elements are parallel-veined leaves that resemble cordaites but that could be isolated pinnules of a pinnate leaf.’

1.1Zoology A part or organ like a small wing or fin, especially a side branch on the arm of a crinoid.

‘It should have required less energy for the crinoid to regenerate the damaged pinnules than to regenerate a lost or damaged tegmen containing part of the gut tract.’

‘Recent crinoids are passive suspension feeders on microscopic plant and animal plankton and organic detritus by means of the tubefeet of the water vascular system in their arms and pinnules.’

‘Their relative inedibility and dense network of arms and pinnules makes crinoids attractive to commensals - organisms which benefit from close association with a host - and other small animals that wish to hide from predators.’

‘The food is transferred down the arms to the mouth by tube feet located on the pinnules and arms.’

‘Fishelson and Nichols observed fish targeting organisms sheltering in the arms and pinnules of living crinoids.’

Origin

Late 16th century (denoting one of the sights of an astrolabe): from Latin pinnula ‘small wing’, diminutive of pinna.